coverage: Store coverage source regions as Span until codegen

compiler/rustc_codegen_llvm/src/lib.rs

@@ -17,6 +17,7 @@
 #![feature(iter_intersperse)]
 #![feature(let_chains)]
 #![feature(rustdoc_internals)]
+#![feature(try_blocks)]
 #![warn(unreachable_pub)]
 // tidy-alphabetical-end